This invention relates to a sensor system for monitoring the movement of particulate elements in a duct system including a plurality of ducts.
One example of an arrangement in which the device of the present invention may be used is that of an air seeder. An air seeder system consists of a large pressurized material tank for seed or fertilizer, a fan, supply tubes going to the seeding equipment and the seeding equipment itself. During operation the fan forces air through the supply tubes which typically run underneath the material tank. Product is metered into the air stream in the tubes carrying the material in particulate form to the seeding equipment. At the seeding equipment, the air stream is divided into smaller tubes each of which is positioned above the location on the machine where a seeded row is to be made. The seeds are then blown into the seed bed as it is prepared by the seeding equipment. Generally this seed bed is prepared by a knife which is drawn through the soil with the seed tube positioned behind the knife so that it deposits the seeds as the knife moves forwardly.
During operation a number of faults can occur which will prevent one or more of the seed tubes from properly supplying the seed to the ground. In some cases the seed tube can become disconnected in which case no seeds will be transmitted through the tube at all. In other cases the seeds may collect within the tube and cause a partial blockage. In other cases soil will enter the lower end of the seed tube and will cause a plugging action so that the seeds are blocked at the point where they enter the ground and while seeds can continue to flow along the tube they collect at the blockage point and are not properly seeded.
While these blockages have been known and occur on a regular basis, it has been difficult to provide equipment which satisfactorily detects the movement of the particulate elements. Many air seeders therefore do not have any detection equipment and hence the operator is not aware of any blockages and many rows can therefore be left unseeded reducing resultant yields.
Various equipment has been provided in an attempt to provide a monitor system which properly detects movement of seeds or other particulate elements through the tubes. Fault conditions where flow of the particles is cut off completely (such as a disconnected hose) are relatively easy to detect. However when a blockage occurs downstream of the sensor in the seed tube, it is possible that seeds will still be carried down the tube. In most cases the sensor provided detects these slow moving seeds and assumes that the tube is operating normally with the seeds flowing to the downstream end for discharge. However one major fault which occurs in air seeding equipment is a blockage at the end of the tube and this blockage would therefore not be detected by a device of this type until the tube is filled up to the sensor. This occurs of course only after a lengthy period of time so that the seeds collected in the tube are generally wasted and rows are left unseeded.
Conventionally the sensors used employ a piezoelectric crystal together with an element which projects outwardly into the duct so that the element is struck by seeds or other particles passing along the duct thus producing in the crystal high frequency ringing signals. These signals are then transmitted to a suitable detection module which analyzes the signals and attempts to indicate when one or more of the tubes is not operating properly.
Examples of systems of this type are shown in U.S. Pat. No. 4,079,362 (Grimm) and U.S. Pat. No. 4,463,345 (Okkerse). The Grimm patent is concerned with the mounting of the piezoelectric crystal and mentions only briefly the system for analysis for the signals produced. The Okkerse patent relates to a system in which the transmission of the signals to the central monitor is carried out by a sequencing unit so as to reduce the period of time necessary for transmission of a fault signal to the central monitor. Neither of these patents addresses the problem of the analysis of the signals to produce a fault signal while particles continue to flow within the duct but at reduced velocity due to a downstream blockage.
U.S. Pat. No. 3,927,400 (Knepler) discloses a further system for counting the number of seeds delivered and comparing that number with a required number. The device uses a photoelectric sensor device which senses the presence or absence of a seed and hence would not be able to detect slow moving seeds caused by a blockage downstream of the detection system.